Conventional bearing apparatus, such as thrust bearings and radial bearings, typically include one or more annular members or bearing rings, such as a rotor and a stator, and a plurality of bearing elements disposed thereon. The bearing elements may be disposed in a single circular array of pockets in each of the annular members. The array of pockets in the annular members may be concentric with the inner and outer edges of the annular member. In operation, two annular members may be aligned with their respective bearing elements facing each other, such that the bearing elements contact one another while one or both of the annular members rotate.
While conventional bearings using superhard material for the bearing elements are capable of sustaining very high loads and speeds in a variety of operating conditions, the bearings are often damaged by heat generated by the friction between bearing elements during operation. If the bearings are not designed to remove generated frictional heat, elevated bearing temperatures may result in bearing failure. For example, when the temperature of a bearing element rises above a certain threshold temperature, the bearing element may begin to degrade.
In down-hole oil and gas drilling applications, this problem has been addressed through the use of cooling fluid. Usually in the form of drilling mud, the relatively cool fluid flows around the bearing elements to cool the bearing elements. Generated frictional heat is transferred from the bearing elements to the cooling fluid by convective heat transfer. The cooling fluid carrying the heat may then be circulated away from the bearing elements. However, because the cooling fluid flows around only the surfaces of the bearing elements, a thermal gradient is created within the bearing elements. That is to say, the center of the bearing elements remain hot while the outer surfaces of the elements are cooled by the cooling fluid. The heat at the center of the bearing elements may still result in bearing failure, and therefore the use of cooling fluid alone has not fully addressed the problem of frictional heat generated by bearing elements.
One possible solution that has been previously postulated is to decrease the size of bearing elements. By reducing the distance from the hot, central portion of the bearing element to the cool, outer portions of the bearing element, the maximum bearing element temperature may be reduced. However, reducing the bearing element size also reduces the total bearing element-to-bearing element contact area of the bearing, thus increasing the pressure on the bearing elements for the same axial load.
Thus, a need exists for an improved bearing capable of reducing or eliminating the effects of frictional heat without significantly increasing the pressure on the bearing elements.